Structures & Foundations


Taking the Stress Out of Cracks

Cracks in the walls are not restricted to homes owned by the Addams Family or Dr. Frankenstein. Cracks are found in most homes, but you'll be glad to know that in most cases, they are not related to structural problems. Approximately 80 percent of the cracks we see in residential structures are horizontal, vertical or diagonal. A large number are minor and do not require repairs outside of some basic caulk and repainting. The following will help you better understand which cracks are potential problems and which are not:

Horizontal Cracks: Horizontal cracks are usually structurally related. However, their significance depends on whether there is lateral movement and, if so, how much. If a wall has moved one-third of its thickness out of plumb, it is in imminent danger of falling. If it has not moved, or if the movement is less than one-third of its thickness, the wall can probably be reinforced.

Vertical Cracks: Vertical or nearly vertical cracks are only structurally related when there is lateral movement (e.g., bow or shear). This assumes the crack is a consistent width from top to bottom. In most cases, vertical cracks are hairline or slightly wider and are caused by normal shrinkage or contraction. Expansion and contraction are normal for building materials. The more rigid the material is, the more likely it is that a crack will develop. Porous or less dense materials will be flexible and less likely to crack. Vertical cracks in a wall with a vertical bow or with sheared wall planes are structurally related. Contraction cracks are hardly ever a structural concern.

Diagonal Cracks: Diagonal wall cracks that break through the building material are almost always structurally related. Step cracks in a block wall that only crack at the mortar joints and not through the block wall are not typically a structural problem, unless lateral movement is present. When the bearing or foundation under a wall is not adequate, the wall will settle or sink at the weak area. The adjacent wall structures that are adequately supported will resist this movement. This situation will typically cause diagonal cracking.

To determine the cause or locate the source of a diagonal crack, draw a line perpendicular to the crack down from the approximate center of the crack. Once you locate and understand the source of the crack, proper corrections will be relatively easy to determine and address.

Cracks in Plaster Ceilings: There are generally two reasons why cracks in plaster ceilings occur:

  1. Over the years, gravity will cause the plaster to crack. Typically, cracks develop in larger ceilings, in the direction of the longer dimension, at approximately 30 to 40 years. Cracks develop perpendicular to the first cracks at approximately 40 to 60 years. The ceiling loosens at approximately 70 to 90 years. Repair or replacement is then necessary.
  2. When the frame structure above a ceiling is not stiff enough to keep the plaster from cracking, premature cracks are inevitable. Excessive weight or bouncing can cause floors to flex and cause plaster on the ceiling below to crack. There are various solutions to these problems. These solutions are influenced by such things as thickness, height and span of the wall; source of the problem; and available space.

If there is a structural problem with any of the cracks explained above, it is recommended that you consult a professional engineer.

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How to Select a Contractor

Need a deck or enclosed porch built, but don't know who to call? Are you new to an area and not familiar with any contractors? Here is some practical advice on what to look for when selecting a contractor:

  1. Ask for references from people you know. This is always the best way to find out who does professional work, prices work fairly and is someone with whom you can work. If this is not an option because you are new to the area, consider these recommendations:
  2. Call a wholesale supplier of materials. If you need a carpenter or general contractor, call a full-service lumber yard. If you need a plumber, mason, roofer, etc., call their respective suppliers for names. The names given to you by the supplier will probably have the following traits or qualities:
    1. Professional: They will probably do professional work because the supplier will not want to stake his reputation on an incompetent contractor.
    2. Responsible: They will probably act responsibly. The supplier is not likely to recommend someone who doesn't pay his bills. The professional relationship the contractor has with the supplier suggests that he may do a lot of business with the supplier. This means the tradesman has valuable experience.
    3. Likeable: They will probably be likable because few will refer people who are not likable.
  3. Call real estate agents, local code enforcers and building trade organizations.
  4. Plan the job well ahead of time, no less than one or two months before the start of work is anticipated, so you can have relaxed interviews with contractors.
  5. Make a list of questions before the meeting. Ask for names, addresses and phone numbers of references of those who have had work done within the past year. The professional contractor should have these on short notice.
  6. Make a list of the things you want the contractor to do. Be as clear as you can, because you want accurate interpretations. Ask the contractors to write comprehensive and exacting specifications in their bids so you can avoid ambiguities.
  7. Ask about availability and scheduling. Also ask for a written time line in the proposal and outline contingencies of action if the work is not completed in that time frame. This is generally not an issue for smaller jobs.
  8. Ask if he likes and can handle your work, including specific type and overall size of the job.
  9. Lastly, and most importantly, determine if you can work with the contractor. You may be working with this contractor for several days, weeks or months. A good rapport is necessary.

Engage him in a conversation about hobbies, goals and attitudes in an effort to determine what type of person he is. This will be very helpful should any problems or questions arise. Having a bond with someone typically makes them more amiable to your reasonable requests. Ask yourself these questions:

  1. Are your personalities compatible?
  2. Is the contractor informative and helpful?
  3. Do you trust him?
  4. Is he developing a good rapport with you?
  5. Does he ``want the work''?

Selecting the right contractor will give you peace of mind in knowing you are getting quality work at a fair price. The time put in at the beginning can give you a professional job that you and the contractor can be proud of.

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How to Repair Damaged Joists

A frequent casualty of termite and/or moisture in homes is damaged joists. These problems may develop in masonry homes where water has penetrated and is absorbed in the masonry and the wood joists or frame homes generally due to moisture or high relative humidity.

Signs of a problem may include: sagging floors, crushed joists at the wood sill or masonry bearing point, and a separation at the floor and joist towards the end of the joist. This situation should be visible in unfinished areas.

It is always better to have a professional contractor do this type of work, but reinforcing joists can be done by even some inexperienced homeowners. Here is a basic plan:

  1. The amount of lumber needed for reinforcement is about 1/3 of the length of the joist plus the amount of damaged wood. If you have a 15’ joist, the replacement piece of wood should be at least 5’ plus the damaged wood. (e.g., if the last 3’ are damaged, the sister joist should be a minimum of 8’ long). Use the same size lumber (e.g., 2" x 8"’s should reinforce 2" x 8"s, etc.).
  2. To support the damaged joist from below with a column or pier, a 4" x 4" is acceptable, if it has adequate footings.
  3. When you install the sister joist, it should bear on the wall a minimum of 4", either in a widened masonry wall pocket or on a wood sill.
  4. To attach the new joists, be sure to use through bolts or, at the very least, lag bolts. These should be staggered up and down, but relatively close to the center of the joists. The bolts should be placed no more than every 18" apart and should have large washers or plates to hold properly. Be sure to drill holes the same size as the bolt to create a snug fit You’ll probably have to hammer the bolt into the wood.

You do not want to use nails because when you put weight on the floor system the joists will flex and twist. When this happens, there is a tendency for the nail to pull or loosen. It only takes 80 lbs. per square inch, (p.s.i.) to pull out a 16-penny nail. Some through-bolts, when used with washers and plates, can support more than 1,000 p.s.i. before a bolt can be pulled through the joists.

If you don’t have the space to use through bolts, we recommend you use lag bolts to give you the lateral strength to hold the pieces of lumber together. If you do the work yourself, the typical costs to repair the joists in this manner is usually $20 per joist for materials. If a contractor does the work, your cost will probably range from $125 to $200.

Hire a structural engineer for any unusual or severely damaged situations as a more comprehensive design solution may be necessary.

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Building Retaining Walls That Last

Retaining walls are found in front, side and back yards all across the country. But, as you would see from a stroll through any neighborhood, many of them are leaning. Not only does this look unappealing, it can also pose somewhat of a hazard. The solution to this is relatively straightforward.

Retaining walls are typically used to hold back soils due to an uneven terrain. Vertical retaining walls, whether masonry or wood, do not have a lot of horizontal strength. They are better designed to receive a vertical load, and this may cause problems. Vertical walls that are bearing weight have some lateral strength because of the weight.

The weight of the soils on one side of the wall provides constant lateral pressure and tends to push, stress and then crack the wall. The amount or height of soil behind the wall is indicated as an unbalanced load.

Retaining walls should be built with portions of the wall going perpendicular to the main wall and into the soil to provide lateral stability. They should be tied to the main wall. Corners and steps also strengthen the wall to a great degree.

Even when lateral stability can be improved, the relentless stress from the unbalanced load causes these walls to move and fail. The main cause of retaining wall problems is ultimately due to water. Water causes soil, like clay, to expand when it absorbs water. This expansion pushes against the wall. Sandy soil presents less of a problem because it is porous and acts somewhat like a drain.

Every retaining wall should have a drainage system behind the wall to carry water away and assure there will not be additional pressure developing from the soils due to water.

The drainage systems should include:

  1. A full-depth trench, 6'' to 12'' wide, behind the wall.
  2. A grade at the bottom of the trench that directs water to drains in the wall.
  3. 1'' to 1 1/2'' stone, filled to approximately 4'' to 6" from the top.
  4. Burlap or felt paper on top of the stone to keep the soil above from filtering into the stone.
  5. Soil and either top soil and seed or sod on top of the paper, approximately 4'' to 6''.

The required thickness of the wall will vary, depending on the unbalanced load. Retaining walls should be a minimum of 12'' thick. If they are five feet high or more, or have special use, they should be reinforced. The design should be provided by a structural engineer.

The cost to build a retaining wall varies based on the size of the wall and materials used. For a four-foot high block wall with foundation, expect to pay approximately $60 per linear foot, including materials and labor. When installed properly, a wall can last decades.

Different materials can be used for retaining walls. Block, brick, stone, concrete or wood retaining walls can be dependable, assuming the design is adequate. The material selection should also match the overall look of the property.

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Terminating Termites

Although they're small, termites can pose a big problem to homeowners. There are some practical ways, however, to reduce their infiltration into your home. You'll be glad to know that none of these terminating measures involves Arnold Schwarzenegger and his battery of firearms.

Subterranean termites live in the soil. Their role in nature is to consume dead trees and debris, to help turn them back into the soil. Unfortunately, though, these termites can't tell the difference between your home's framing lumber and the dead tree in your backyard. In fact, some frustrated homeowners may even say that the termite likes the taste of a home better than the tree. But that point is arguable. Nevertheless, termites are hard to keep out of the house if there is an environment that will support them, such as high relative humidity.

Termite shields do not keep them out. They can crawl through seam laps. In fact, they only need 1/32 of an inch to get through. Termites can even get through minute cracks in a block wall and climb up the hollow blocks to the wood areas. Because builders throw debris in the back fill, there is often a lot of good eating.

Houses where the siding touches the grade (it should be 8'' above the grade), slab houses, and below the grade window frames in window wells are vulnerable. Termites are found at or near ground level and seldom are they found above the first floor.

Termites must return to the soil regularly due to the moisture in the soil that they need. The oxygen in our air will cause the termites to weaken and die. There is less oxygen in the soil and they are better suited to the soil environment. This situation tends to restrict their movement too far from the soil.

The way to keep termites under control is to prevent them from getting to the structure or from reaching moisture. There are two basic types of control:

  1. Mechanical method: This method seeks to physically alter the building to prevent earth-to-wood contact. You should also control moisture around the home by changing the grade, installing downspout extensions, repairing leaks quickly, installing footing drains, and drying up a wet crawl space. These moisture-reducing procedures will also reduce the probability of termite entry.
  2. Chemical method: This method seeks to create a chemical barrier around the structure that the termites cannot penetrate. There are two types of chemical control: pre-construction and post-construction.

Pre-construction is the best and most effective because there is more access to the soil and a more complete chemical barrier can be set up. In addition, the soil under the slab can be pre-treated as well. For those buying new construction, be sure to ask the builder to treat the soil.

Post-construction is more difficult because you must work around the existing structure. It is not possible at all times to chemically treat some areas of the pre-existing building. The end result is often limited success. This means you need to rely heavily on changing the environment (i.e., reducing moisture, etc.).

Some chemicals that are used in soil poisoning are Heptachlor, Aldrin and Dursban T.C. There are also numerous synthetic chemicals on the market. Chlordane was the chemical of choice for decades until it was banned in 1985, due to installation problems and an occasional poisoning from off-gassing. It was the most effective chemical used for this purpose because it would crystalize in the soil and remain stable for decades.


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